Have you discussed this with your Pulmonologist? Could this be from the way you are standing or working? Are you using good lifting posture? Recently I started Rehab and found myself holding my breath while I did some of the exercises. Are you doing anything like that? Are you wearing the correct shoes for the work you are doing? Could be a lot of things.
I have gotten lower back pain. I also hurt a lot being on my feet to long. So I prop my feet and try to limit the length of time I stand. Maybe we are clogged in our legs., I will ask one of several Dr. I have. If I find anything I will share with you. Blessings to you. I know how back pain feels. OUCH!